The processing of optically active surfaces of spectacle lenses by machining can be roughly divided into two processing phases, namely initially the preliminary processing of the optically active surface for producing the macrogeometry according to prescription and then fine processing of the optically active surface in order to eliminate preliminary processing tracks and to obtain the desired microgeometry. Whereas preliminary processing of the optically active surfaces of spectacle lenses is carried out inter alia in dependence on the material of the spectacle lenses by grinding, milling and/or turning, the optically active surfaces of spectacle lenses in the case of fine processing are usually subjected to a fine grinding, lapping and/or polishing process, for which purpose use is made of an appropriate machine.
Manually loaded polishing machines in RX workshops are, in particular, usually constructed as “twin machines” so that advantageously the two spectacle lenses of an “RX job”—a spectacle lens specification always consists of a spectacle lens pair—can be subjected to fine processing simultaneously. Such a “twin” polishing machine is known from, for example, the specifications US-A-2007/0155286 and US-A-2007/0155287.
In this previously known polishing machine two parallelly arranged workpiece spindles, which are each rotationally driven about a respective axis of rotation, but which are otherwise stationary, project from below into a work space where two polishing tools are disposed opposite thereto, so that one polishing tool is associated with one workpiece spindle and the other polishing tool is associated with the other workpiece spindle. Each polishing tool is freely rotatable by way of a spherical bearing at a piston rod, which projects from above into the work space, of a respectively associated piston/cylinder arrangement, which is arranged above the work space and by which the respective polishing tool can be individually lowered or raised with respect to the associated workpiece spindle. The two piston/cylinder arrangements are additionally movable in common by a linear drive forward and back with respect to a front side of the polishing machine in a direction perpendicular to the axes of rotation of the workpiece spindles and, moreover, tiltable in common by a pivot drive about a pivot axis, which similarly extends perpendicularly to the axes of rotation of the workpiece spindles, but parallel to the front side of the polishing machine. The angular position between the axes of rotation of the tools and workpieces can be preset by the pivot drive before the tools are lowered by the piston/cylinder arrangements onto the workpieces. During the actual polishing process the workpieces are rotationally driven, in which case the tools disposed in processing engagement with the workpieces are rotationally trained by friction, while the linear drive ensures that the tools are moved alternately forward and back with respect to the front side of the polishing machine so that the tools continuously wipe back and forth over the workpieces with a relatively small travel (so-termed “tangential kinematics”).
The advantages of this “twin” polishing machine include that it is constructed from economic components in simple manner in terms of hardware, it is very ergonomic for manual loading and, in addition, by virtue of its extremely compact, very narrow construction requires very little set-up area in the RX workshop. However, it would be desirable if other polishing methods could also be carried out on such a polishing machine. Thus, for example, the flexible polishing tools disclosed in the specifications EP-A-1 473 116, EP-A-1 698 432 and EP-A-2 014 412 are designed for polishing methods in which apart from the workpiece, also the tool itself is rotationally driven, whereby the polishing times are significantly shortened by comparison with polishing methods in which the tool is entrained merely by friction.
The polishing device disclosed in DE-A-102 50 856, (see FIGS. 5 to 9) has an electric rotary drive for the polishing tool, which as such comprises a stator and a rotor, and with a pneumatic piston/cylinder unit for axial deflection of the polishing tool along a longitudinal axis. In this regard, the arrangement of the rotary and axial drives is such that a spindle-shaft subassembly (“rotor” in the language of the above-mentioned specification), which is mounted in a housing to be rotatable about an axis of rotation and which carries the actual polishing tool at its end protruding out of the housing, is rotationally driven by way of a cogged belt drive by the electric rotary drive, which is arranged in the housing to be laterally offset parallel to the axis of rotation. The pneumatic piston/cylinder unit and an associated axial guide are, thereagainst, integrated in the spindle/shaft subassembly, consequently rotationally driven therewith, for which reason the piston/cylinder unit needs, for pressure medium feed, a compressed air rotary leadthrough. This polishing device requires a relatively large amount of installation space, for which reason it is not suitable for use in the afore-described “twin” polishing machine.
Finally, disclosed in specification DE-A-10 2009 041 442—which was published subsequently—of the same applicant is a device for fine processing of the optically active surfaces at, in particular, spectacle lenses, with a spindle shaft, which has a tool mounting section and which is mounted in a spindle housing to be rotatable about a tool axis of rotation, an electric rotary drive, which comprises a rotor and a stator and by which the spindle shaft operatively connected with the rotor is drivable to rotate about the tool axis of rotation, and an adjusting device, by which the tool mounting section is axially displaceable with respect to the spindle housing in the direction of the tool axis of rotation. A feature of this device is that the rotor and the stator are arranged coaxially with the spindle shaft, in which case by the adjusting device at least the rotor together with the spindle shaft is axially displaceable with respect to the spindle housing in the direction of the tool axis of rotation, which, in particular, gives rise to a very compact construction.
However, in the case of very strong curvatures or larger changes in curvature over the circumference of the processed optically active surfaces, which require greater axial strokes at the tool, the use of this device finds its limits. Since the spindle shaft and rotor—which have a not inconsiderable mass—have to be moved in company with the respective axial stroke, rapid axial compensating movements, which might be required, of the tool are not possible.
What is needed is a polishing device having a simple and economic construction for fine processing of optically active surfaces at, in particular, spectacle lenses What is further needed is a polishing device by which a polishing tool can be rotationally driven as well as axially displaced—in which case the tool shall also be capable of executing rapid axial compensating movements—and which nevertheless is very compact, so that it can be used in, for example, “twin” polishing machines of very narrow construction such as, for example, the polishing machine described in the introduction.